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Avalanche Forecast

Archived

Jan 11th, 2021–Jan 12th, 2021

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Coast Inland.

 Natural avalanches are expected on Tuesday with reactive slabs at higher elevations and loose wet avalanches below. The snow will load buried weak layers and could produce very large slab avalanches.  

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain. We are confident the likelihood of avalanche will increase with the arrival of the forecast weather. Uncertainty is due to difficult to forecast freezing levels.

Weather Forecast

Yet another strong Pacific frontal system is slated to hit the Coastal regions tonight and persist until Wednesday morning bringing rising freezing levels, heavy precipitation, and strong to extreme wind. There will likely be a division in this region with the Coquihalla seeing heavier precip, while the Duffy sees a bit less as it falls as snow. Regardless, Tuesday will see significant weather.

Monday Night: Snow 5-10 cm (up to 20 mm on the Coquihalla) with freezing levels near 1300 m. Alpine temperatures near -2 and ridgetop wind strong from the south- southeast.

Tuesday: Snow 10-25 cm (30-45 mm on the Coquihalla) with freezing levels rising to 2000 m. Alpine temperatures near 0 degrees with strong to extreme ridgetop wind from the southwest. 

Wednesday: Generally a drying and cooling trend bringing a mix of sun and cloud. Alpine temperatures near -4 and light southwesterly wind. Freezing levels near 900 m. 

Avalanche Summary

On Monday, no new avalanches were reported at the time of publishing this forecast.

Two large avalanches were observed near Duffey Lake on Saturday, described here and here. It is suspected that both avalanches were triggered naturally and on the weak layers described in the snowpack summary. Also, a notable skier-triggered avalanche occurred near Whistler, not far from this region (see the Sea to Sky bulletin for more info).

Snowpack Summary

New and reactive storm and wind slabs will continue to build Tuesday. The storm is expected to drop around 15 cm Monday night and another 20-30 cm Tuesday. The storm will come with strong southwest wind so wind slabs are expected at higher elevations. Treeline and below treeline elevations may see a loose wet avalanche cycle where the precipitation falls as rain. In sheltered areas, this snow may overlie surface hoar. The higher snow amounts mentioned above are forecast for the Coquihalla with less expected in the North (Duffy, Hurley).

A melt-freeze crust from early December is found around 80 to 180 cm deep in the snowpack. This crust may have surface hoar or sugary faceted grains sitting above it. This persistent weak layer is most prevalent in the north (e.g., Duffey Lake, Hurley).

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • Watch for fresh storm slabs building throughout the day.
  • Be aware of the potential for large avalanches due to the presence of buried weak layers.
  • Avoid exposure to overhead avalanche terrain, avalanches may run surprisingly far.
  • The more the snow feels like a slurpy, the more likely loose wet avalanches will become.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.